I don't have a specific idea in mind, but p5.js is a fantastic library that just begs to be used in a htmlwidget. Some 'prior art':

geom_realtime(): live-plotting microphone input: https://www.youtube.com/watch?v=3mdiCUbgxi0

click and animate: https://www.youtube.com/watch?v=BRYlPWEtVQ8

The examples page linked above has many, many possibilities.